Sound
is the compression and rarefaction of sound waves traveling through a
medium such as air. An initiating disturbance compresses air
molecules which then rarefact and then compress in a continuing cycle
until it terminates in our ears or fades ... This is the cycle of
sound.

Handbook Note:Hertz
(Hz)
= a unit of measurement of cycles per
second.
One
thousand =
one kilo or K
KHz
= one thousand Hertz
One
million =
one Meg, Mega or M
MHz
=
one million Hertz

Sound
engineers have translated sound
waves into measurable illuminated lines on the screen of an
oscilloscope. The modulating lines illustrate the
amplitude, wavelength, and
frequency of a sound wave.

The
oscilloscope reveals a ten-octave frequency
range of sound that spans from 20Hz to 20KHz. The area of 20Hz to about 200Hz includes low
frequency bass. The
human voice and many musical instruments occupy
the region of approximately 200Hz to 1KHz. The balance of the frequency
range includes the
harmonics of sound such as the reverberations of a guitar, piano, bell, cymbal, etc.

Handbook
Note: The
speed of sound = 1130
ft/second

The wavelengthsof
sound can be computed by dividing the speed of sound by the frequency.
For example; 20 cycles per second has
a wavelength of 56.5 feet (1130÷20) and
20KHz has a wavelength of about 0.678
of an inch (1130÷20K). The
amplitude or objective volume level of
sound is measured in the
logarithmic units of sound
pressurecalled a decibel (db). It
is a scale that extends from 0db to 194db.
A logarithmic
scale is employed because of the immense range of the human
ear that spans from the threshold of hearing to beyond the threshold
of pain.
The threshold of
hearing is the level created by a molecule of
air landing on the surface of the eardrum. You read that
right. The
threshold of pain is at about the sound pressure level
created by a large
aircraft during takeoff at close range.
(120db)

In
the 1930s, Bell
Labs researchers Fletcher
and Munson observed that
the subjectiveresponse
of the human ear differed from the objective measurement of sound
pressure level. They
determined that the human ear is most sensitive
to the range of 1KHz to 5KHz. Frequencies above and below must be
increased in volume to be perceived as loud. The effect
becomes
more prominent as the
volume is decreased. The effect diminishes as the volume
is increased. Fletcher and Munson defined
this subjectiveor
psycho-acoustical response to sound as loudness.

Handbook
Notes:A
doubling
of loudness = about a 9 to10
decibel change
in sound pressure level.
A
doubling
of amplified power
creates an increase of about 3db.
Speed
of sound = 1130
ft/second at
sea level.
Frequency
range of audible sound = 20
Hz to 20KHz
Range
of audible wavelengths = 56.5
ft. to 0.678 in.
Threshold
of hearing =0
db
Threshold
of pain = approximately 120
db
Sound
can also travel through other media such as water, wood, steel, etc., but
it cannot travel
through a vacuum such as the vacuum of
outer space.